CCR2 in Hematopoietic Stem Cell Homing, Macrophage Polarization and Organ Repair

描述（由申请人提供）：造血干细胞（HSC）和祖细胞（HPC）是产生终末分化循环血细胞的骨髓源性细胞。最近的研究表明，这些细胞在炎症环境中参与了实质组织的修复，但调节这种运输的信号却知之甚少。在其他NIH资助的工作中，我们发现并克隆了CCR 2，一种调节单核细胞向MCP-1迁移的趋化因子受体，并表明CCR 2-/-小鼠在动脉粥样硬化小鼠模型中受到保护。在初步的未发表的结果中，我们现在发现CCR 2在原始HSC的亚群以及一些髓样HPC上表达。CCR 2介导c-Kit+Lin-骨髓衍生细胞对MCP-1和MCP-3的趋化性。在滴注巯基乙酸盐WT后，而不是CCR 2-/-干细胞被主动募集到腹膜，并且在施用对乙酰氨基酚后被募集到肝脏。值得注意的是，输注CCR 2 +/+而不是CCR 2-/-HSC/HPC加速了肝损伤的消退，并且募集的细胞表达M2巨噬细胞表型的特征性基因。基于这些最近的发现，我们提出了三个相互关联的具体目标，以确定CCR 2在HSC/HPC运输中的作用，以及它们在炎症和损伤的解决中的潜在作用。在特异性目的1中，我们将定量早期造血干细胞上CCR 2的表达。我们将检验CCR 2在真实的、自我复制的干细胞上表达，并介导它们对组织炎症和损伤部位的趋化性的假设。使用新型CCR 2/RFP敲入小鼠，我们将定量小鼠造血树所有分支中HSC/HPC上CCR 2的表达，并确定CCR 2的激活是否动员骨髓中的HSC和HPC。在具体目标2中，我们将确定CCR 2介导的HSC或HPC募集是否有助于急性（对乙酰氨基酚）和慢性（四氯化碳）诱导的肝毒性模型中炎症和缺血性损伤的消退，将确定募集的干细胞和祖细胞的命运，并将测试以下假设：富集表达CCR 2的HSC/HPC将显著增强组织修复。在《特定目标3》中，我们将把注意力转向小鼠实验性心肌梗死模型，并将确定CCR 2+或CCR 2-HSC/HPC是否加速心脏功能恢复，以及CCR 2拮抗剂是否减少炎症并增强功能恢复。上述工作的完成将确定调节骨髓干细胞和祖细胞归巢到损伤组织的信号，并进一步加深我们对它们在组织修复和再生中作用的机制理解。

DESCRIPTION (provided by applicant): Hematopoietic stem cells (HSCs) and progenitors (HPCs) are bone-marrow derived cells that give rise to terminally differentiated circulating blood cells. Recent work has implicated these cells in the repair of parenchymal tissue in the setting of inflammation, but the signals that regulate this trafficking are poorly understood. In other NIH funded worked we discovered and cloned CCR2, the chemokine receptor that regulates monocyte migration to MCP-1, and showed that CCR2-/- mice are protected in murine models of atherosclerosis. In preliminary, unpublished results we have now found that CCR2 is expressed on subsets of primitive HSCs as well as some myeloid HPCs. CCR2 mediates the chemotaxis of c-Kit+Lin- bone marrow derived cells to MCP-1 and MCP-3. Following instillation of thioglycollate WT, but not CCR2-/- stem cells were actively recruited to the peritoneum, and to the liver following administration of acetaminophen. Significantly, infusion of CCR2+/+, but not CCR2-/- HSCs/HPCs accelerated the resolution of liver damage, and the recruited cells expressed genes characteristic of the M2 macrophage phenotype. Building on these recent findings, we propose three interrelated specific aims to define the role of CCR2 in HSC/HPC trafficking, and their potential roles in the resolution of inflammation and injury. In Specific Aim 1 we will quantify expression of CCR2 on early hematopoietic stem cells. We will test the hypothesis that CCR2 is expressed on true, self-replicating stem cells, and mediates their chemotaxis to sites of tissue inflammation and injury. Using novel CCR2/RFP knock-in mice, we will quantify the expression of CCR2 on HSCs/HPCs in all branches of the hematopoietic tree in mice and determine whether activation of CCR2 mobilizes HSCs and HPCs from bone marrow. In Specific Aim 2 we will determine whether CCR2-mediated recruitment of HSCs or HPCs contributes to the resolution of inflammation and ischemic injury in models of acute (acetaminophen)- and chronic (carbon tetrachloride)-induced hepatotoxicity, will determine the fate of the recruited stem and progenitor cells, and will test the hypothesis that enriching HSCs/HPCs for those that express CCR2 will significanlty enhances tissue repair. In Specific Aim 3 we will turn our attention to a model of experimental myocardial infraction in mice, and will determine if CCR2+ or CCR2- HSCs/HPCs accelerate recovery of cardiac function, and whether CCR2 antagonists reduce inflammation and enhance functional recovery. Completion of the work described above will identify the signals regulating the homing of bone marrow stem and progenitor cells to injured tissue, and further our mechanistic understanding of their role in tissue repair and regeneration.